The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation adapted for inserting a spinal implant within the intervertebral disc space between adjacent vertebra. More particularly, while aspects of the invention may have other applications, the present invention is especially suited for disc space preparation and implant insertion into a disc space from an anterior surgical approach to the spine.
Various surgical methods have been devised for the implantation of fusion devices into the disc space. Both anterior and posterior surgical approaches have been used for interbody fusions. In 1956, Ralph Cloward developed a method and instrumentation for anterior spinal interbody fusion of the cervical spine. Cloward surgically removed the disc material and placed a tubular drill guide with a large foot plate and prongs over an alignment rod and then embedded the prongs into adjacent vertebrae. The drill guide served to maintain the alignment of the vertebrae and facilitated the reaming out of bone material adjacent the disc space. The reaming process created a bore to accommodate a bone dowel implant. The drill guide was thereafter removed following the reaming process to allow for the passage of the bone dowel which had an outer diameter significantly larger than the reamed bore and the inner diameter of the drill guide. The removal of the drill guide left the dowel insertion phase completely unprotected.
More recent techniques have advanced this concept and have provided further protection for sensitive tissue during disc space preparation and dowel insertion. Such techniques have been applied to an anterior approach to the lumbar spine.
An initial opening or openings are made in the disc space and the height of the disc space is distracted to approximate normal height. Typically, a first distractor is inserted with a height estimated by radiological examination. If additional distraction is required, the first distractor is removed and a second, larger distractor is inserted. However, since the positioning of the distractors is performed without the benefit of protective guide sleeves, the switching of distractors increases the potential for damage to neutovascular structures and may correspondingly increase the time of the procedure.
For bilateral procedures, a double barrel sleeve may be inserted over the distractors, with a central extension extending into the disc space to maintain distraction. One limitation on guide sleeve placement is the amount of neurovascular retraction that must be achieved to place the guide sleeves against the disc space. For some patients, a double barrel sleeve may not be used because there is insufficient space adjacent the disc space to accept the sleeve assembly. Thus, there remains a need for guide sleeves requiring less neurovascular retraction for proper placement and providing greater protection to adjacent tissue.
While the above-described techniques are advances, improvement is still needed to reduce the procedure time by utilization of improved instruments and techniques, to reduce the potential for damage to sensitive tissue adjacent the disc space, and to limit the amount of vessel retraction necessary to utilize the protective instrumentation. The present invention is directed to this need and provides more effective methods and instrumentation for achieving the same.
The present invention relates to methods and instrumentation for vertebral interbody fusion. In one aspect of the invention, the instruments define a reduced width configuration that allows bilateral insertion of implants into the disc space.
In one aspect of the invention, a distractor is provided that includes a distractor shaft with a length. A distractor tip extends from on end of the shaft. The distractor tip has opposite first and second surfaces that define a distraction height between the surfaces. The distractor tip has a recessed area, preferably a concave surface, that extends between the first and second surfaces. Optionally, the distractor shaft may include a recessed area along its length that is an extension of the recessed area of the distractor tip. The recessed area of the distractor and/or shaft may permit the passage of and rotation of surgical devices adjacent thereto.
In another aspect of the present invention, a guide sleeve has a wall that defines a protected passageway to a distracted disc space. The guide sleeve includes a proximal end and a distal end. A pair of overlapping working channels extends between the ends. The sleeve has a first width at the proximal end and a second width at the distal end. The first width is greater than the second width. The reduced second width is provided by reducing the exterior wall thickness of the sleeve at the distal end. Preferably, a first flange and a second flange extend from the distal end at the reduced wall thickness portions. Preferably, the flanges have a thickness that corresponds to the reduced wall thickness. Still more preferably, the first and second lateral extensions have a height less than the height of the distracted disc space, and inhibit encroachment of adjacent tissue into the distracted disc space. In another form, the guide sleeve may include spikes projecting from the sleeve distal end between the flanges to engage the adjacent vertebral bodies. In a further form, the overlapping working channels are substantially cylindrical.
In another aspect, there is provided a guide sleeve assembly. The assembly includes a sleeve defining a working channel. A first distractor has a first distractor tip with a recessed area along a portion of its length, and a second distractor has a second distractor tip. With the first distractor disposed in the working channel of the sleeve in side-by-side relation with the second distractor, the recessed surface of the first distractor tip receives at least a portion of the second distractor tip. In one form, the recessed area of the first distractor tip is defined by a concave surface and the second distractor tip has opposite convex surfaces, one of which is positioned adjacent the concave surface of the first distractor tip. In another form, the first and second distractors define an overlap region in the guide sleeve working channel.
In a method according to the present invention, access is gained to a disc space. A first distractor having first distractor tip with a recessed area and a second concave distractor having a second distractor tip are disposed in side-by-side relation with the distractor tips inserted adjacent the disc space. Preferably, the distractors are also engaged within the working channel of an outer sleeve. The distractors distract and maintain the disc space at the desired height during the procedure. Once the desired distraction of the disc space has been achieved, the outer sleeve is advanced toward the disc space until disposed adjacent the disc space. If necessary, a driving cap may be positioned over the proximal end of the outer sleeve to apply a driving force thereto.
The outer sleeve is then driven into position so that opposing side flanges are positioned in the disc space and spikes on the outer sleeve enter the vertebral bodies. Preferably, the side flanges do not perform any distraction of the disc space. Once the outer sleeve is positioned, the second distractor may be removed and a substantially cylindrical working space is provided through the sleeve to the disc space adjacent the first distractor. Preferably, the working space defines an area that is greater than one half of the area of the working channel of the guide sleeve.
Various surgical procedures are performed through the working space, such as reaming, tapping and inserting a threaded implant into the disc space. Once the first implant is inserted, the second distractor is removed, and the first implant maintains the disc space distraction and defines a working space adjacent the inserted implant. Preferably, the first implant has a concave side wall to define a portion of a substantially cylindrical working space. The surgical procedures are then repeated to insert a second implant adjacent the first implant. In one embodiment, the second implant has a circular cross-section. In another embodiment, the implant has a cross-section that mirrors that of the first implant after insertion.
Although various sleeves are known in the art, in a preferred embodiment, outer sleeves according to the present invention have a reduced width portion adjacent the bone engaging distal end to limit the amount of retraction of the surrounding vasculature and neural tissue required for the procedure. The reduced width portion, preferably in combination with the previously described overlapping working channels, combine to greatly reduce the overall width of the sleeve. In a preferred form, a sleeve assembly includes a pair of opposite side flanges or lateral extensions having a first height. The lateral extensions provide protection from encroachment of tissue into the working area of the disc space. Preferably, the side flanges of the outer sleeve are not used to maintain distraction of the disc space and thus do not experience the forces of disc space distraction. As a result, the flanges and adjacent side walls may be formed with a reduced wall thickness.
A further aspect includes the provision of a visualization window along the centerline of the outer sleeve for visual access to the interior working channel while instruments are in the working channel. Even without the use of an imaging system, the present invention contemplates the use of manually adjustable depth stop that is to control the steps of trephining, reaming, tapping, and implant insertion. The term implant is used in a broad sense throughout the disclosure and is intended to encompass bone dowels, metallic cages and spacers, and other implants used for interbody fusion regardless of shape or material of construction.
Related objects, advantages, aspects, forms, and features of the present invention will be apparent from the following description.